Natural gas is a very good feedstock for conversion to liquid fuels all by itself. If natural gas is available conversion to liquid fuels using natural gas and coal is more efficient than using either natural gas or coal alone. A nuclear - natural gas - coal process would work nicely as well.
Synthesized liquids would require little new infrastructure compared to compressed natural gas and so would be less expensive and more quickly brought on line. Not that natural gas isn’t a good engine fuel, for it certainly is.
This stuff is utterly mundane, no pie in the sky thing, and ready to go right now.